1. Field of the Invention
The present invention is directed to a method for removing or decreasing an iron-caused yellow color from a solution. More particularly, this invention is a process for removing or decreasing the amount of iron-caused yellow color in calcium bromide completion fluids such as those used in oil or gas wells by adding a relatively small amount of alugenite.
2. Description of the Prior Art
Clear, high density brines such as calcium bromide fluids are used in oil well completions and workovers. They are also used as oil well packer fluids. Packer fluids are the fluids which are left in the annular space between the tubing and casing of oil wells. The primary purpose of these fluids is to balance the pressure in the well so as to prevent a well "blow out" without losing the fluid to the formation, and without damaging the formation as is done when solids-laden fluids are used. The densities required by these brines are determined by the well pressures and depths.
Oil well brines are usually prepared by blending different amounts and types of salt solutions to get the required density and composition at the lowest cost. Such brines must be clear, that is, free of solids or solids-forming materials. Sometimes these brines have color immediately after preparation and the amount of color may increase with time. Alternatively, color can be acquired upon aging or upon blending various brines. Brines are oftentimes blended to obtain a desired density. The cause of the color is not always apparent. Color related problems may have originated in the brine manufacturing process or impurities of some type may be "picked-up" during shipping, storing, handling or during the use of the brine "down-hole" in a hot oil well. Sometimes the color problem arises because of ferric ions in the brine.
The problem of color removal in calcium bromide brines is of particular interest. Calcium bromide brines can be prepared in a number of ways yet, generally, some degree of color is imparted to the brine irrespective of the exact method of preparation. Metal bromides such as calcium bromide can be prepared by contacting a basic alkaline earth metal compound in an aqueous medium with bromine in the presence of a lower alkanol as a reducing agent. Calcium bromide brines can also be prepared using hydrogen bromide and lime.
U.S. Pat. No. 4,083,942 discloses the preparation of alkali and alkaline earth metal bromides by reacting a basic compound of an alkali or alkaline earth metal with a reducing agent in the presence of water followed by the addition of alternate portions of bromine and a basic compound while maintaining the pH at less than 7.0.
More recently, it was disclosed in U.S. Pat. No. 4,248,850 that alkali and alkaline earth metal bromides could be prepared by contacting in an aqueous medium a basic metal compound and bromine in the presence of added formaldehyde as a reducing agent.
In U.S. Pat. No. 3,431,068, there is disclosed a method of preparing alkali metal halides but not alkaline earth metal halides by reacting an alkali metal hydroxide with an elemental halogen in a liquid, saturated aliphatic or alicyclic alcohol or ketone, or a saturated aliphatic aldehyde. According to this process, the formation of unwanted halate salt by-products associated with alkali metal halide production is diminished or eliminated.
In making calcium bromide from lime and hydrogen bromide, or lime plus bromine and a reducing agent, the solution is made strongly acid to remove any traces of calcium hydroxide from the lime residue of aluminum, silicon or hydrated iron oxides. Upon neutralizing with caustic or lime, ferric ions in solution precipitate as Fe(OH).sub.3 and are removed by filtration, generally leaving a color free solution. Sometimes an undesirable yellow color persists. Such color may occur because the Fe(OH).sub.3 is colloidal, or because the process of nucleation and/or coagulation to form particles sufficiently large to be removed by filtration may be very slow in such non-ideal solutions.
It is economically advantageous to treat new or used metal bromide solutions in a manner which eliminates color. U.S. Ser. No. 408,035 filed Aug. 13, 1982 now U.S. Pat. No. 4,472,285, claims the use of zinc metal to remove color causing iron impurities from a brine. Sodium borohydride may also be used to decolorize the brine. It is desirable to keep these completion fluids clear and colorless with minimal cost.
Such solutions to the color problem have disadvantages in that they are expensive and/or troublesome.
Accordingly, an object of the present invention is to remove or decrease iron-caused yellow color from solutions such as a brine.